Tuesday Commenter App Roundup

What new app did you find this week that you want to share? Addictive game, helpful tool, or something completely different?

Rules:

1. Please form your responses with: [OS] App Name that links to app store location.
2. Links! We are lazy!
3. ONE app only per week, please. Do you like a few? Come back next week and submit your 2nd.You can choose whatever OS you like. iOS, Android, OS X, Windows, whatever.

Example:

[Android] Google Authenticator - Tool for helpful using 2-factor authentication. I've recently renabled it and hopefully I will keep using it.